The short version
- Cold water and nothing tripping usually means a burnt-out element, a failed thermostat, or the thermostat's safety cut-out has tripped.
- Earth leakage tripping usually means a cracked element or water where it shouldn't be, in the element compartment or the isolator switch.
- Lukewarm water that runs out fast points to a scaled or failing element, or a thermostat that's set low or failing.
- Scalding water or hot water from the overflow pipe means a thermostat stuck on. Switch the geyser off at the DB board.
- Check the breaker, the isolator and any timer yourself. Don't open the element cover or keep resetting a tripping earth leakage.
An electric geyser is a simple machine. A thermostat switches an element on and off to keep a tank of water at a set temperature, and an earth leakage unit on your DB board cuts the power if electricity escapes where it shouldn't. When you lose hot water, one of those three things has almost always failed, and the way it failed leaves a clear sign.
Working out which one it is saves a lot of guesswork. It tells you whether you're looking at a quick part swap or something more serious, and whether it's safe to leave the geyser on in the meantime.
Check these before you call anyone
A surprising number of "broken" geysers are simply switched off. These checks need no tools and don't involve touching anything live.
- The breaker on the DB board. The geyser normally has its own breaker, usually labelled. If it has tripped, note whether it trips again when you switch it back on, because that tells you a lot (see below).
- The earth leakage unit. This is the wider switch on the DB board that cuts a whole group of circuits. If it tripped and the geyser is on that group, the geyser may be the cause.
- The isolator switch. SANS 10142-1 requires a double-pole switch disconnector for the geyser, often in the roof near the geyser or on a nearby wall. Make sure it hasn't been switched off.
- Any timer or smart controller. A mechanical timer stops while the power is off, so after an outage its clock runs behind and the geyser may be switching on at the wrong times. Smart controllers can lose their connection or their schedule.
- Whether it has had time to heat. Heating a full 150 litre tank from about 15°C to 60°C takes roughly 7.9 kWh of energy. On the standard 3 kW element that's about two and a half hours, and a bit longer in practice because of heat loss. If the geyser was off all day, give it that long before deciding it's faulty.
- Whether it's every hot tap or just one. If one tap runs cold and the rest are hot, the problem is that tap or its pipe, not the geyser.
Match the symptom to the part
If the basics check out, the symptom narrows it down quickly:
- Cold water, and nothing trips. The element has burnt out, the thermostat has stopped sending it power, or the thermostat's safety cut-out has tripped. Nothing is leaking current, so nothing trips. The tank just stops heating.
- The earth leakage trips when the geyser switches on, or after it has been heating for a while. Current is escaping to earth. The usual culprits are a cracked element sheath and water in the element compartment or the isolator.
- The geyser's own breaker trips, but the earth leakage doesn't. That's overcurrent rather than leakage, which points to a short circuit in the element or the wiring. Leave it off and have it tested.
- Warm but never hot, or the hot water runs out much faster than it used to. Kwikot lists both as signs of a failing element. A heavily scaled element and a thermostat set too low or failing produce the same symptoms.
- Scalding water at the taps, or hot water or steam from the overflow pipe outside. The thermostat has stuck on, so the element never switches off. Switch the geyser off at the DB board straight away. The safety valve on a Kwikot geyser opens if the water passes 94°C, and that valve is all that's preventing something worse.
How a geyser element fails
Kwikot rates geyser elements by tank size: 2 kW for 50 to 100 litre tanks, 3 kW for the 150 litre geyser that most homes have, and 4 kW for 200 to 250 litre tanks.
The element sits in the water, but it is electrically insulated from it. It fails in one of two ways, and they look completely different from the outside:
- It burns out (open circuit). The heating wire inside breaks, no current flows and nothing heats. Because no current is escaping, nothing trips. You simply have cold water.
- The sheath cracks. Kwikot puts it plainly: "A cracked element sheath lets current reach the water." Current now flows into the tank and down to earth, and your earth leakage unit trips. Under SANS 10142-1 a geyser circuit must be protected by earth leakage that trips at 30 mA or less, a tiny current, so even a small crack is enough. Some failing elements only leak once they have heated up, which is why a geyser can trip a while after switching on rather than immediately.
Scale speeds up both failures. In Kwikot's words, minerals in hard water "bake onto the element surface". The scale insulates the element, so it runs hotter to get the same heat into the water, and it fails sooner.
What a plumber actually measures
With the power isolated, the element's resistance tells you whether it's intact. Worked out from its rating at 230 V, a healthy element reads about 26 ohms for 2 kW, 18 ohms for 3 kW and 13 ohms for 4 kW. No reading at all means it has burnt out. A second test, between the element and the tank's earth, shows whether current is leaking through a cracked sheath. Neither test should be done on a live geyser.
How a geyser thermostat fails
The thermostat is the switch between the power supply and the element. It fails in two directions:
- Stuck off. It never sends power to the element, so the water stays cold. From the outside this looks exactly like a burnt-out element.
- Stuck on. It never cuts the power, so the element keeps heating. That's the dangerous one, and the one that sends hot water out of the overflow pipe.
Kwikot's own test separates the two cold-water faults. With a tester on the element terminals: power at the terminals and cold water means the element has failed; no power at the terminals and cold water means the thermostat has failed. Kwikot specifies that this procedure must be carried out by a qualified plumber or installer, because it means working on live terminals.
The safety cut-out and its reset button
Many geyser thermostats, including Kwikot's KWIKTHERM, have a safety cut-out with a reset button. On the KWIKTHERM, the cut-out trips and the reset button pops if any of these happen:
- the water goes above 104°C
- a power surge or fluctuation goes above the thermostat's 20 amp rating
- an electrical connection is poor
- an element too big for the 20 amp thermostat has been fitted
That list is the reason not to just press the button and walk away. Every item on it is a cause, and resetting the button fixes none of them.
Not heating after a power cut or load-shedding
If the geyser stopped working right after the power came back, three things are worth knowing. First, power coming back on can trip breakers and the earth leakage, so check the DB board before anything else. Second, a surge above 20 amps is on Kwikot's list of things that trip the thermostat's safety cut-out, which leaves the geyser with power but no heat. Third, a mechanical timer will have stopped during the outage and now runs behind.
Eskom's own advice is to switch off geysers, pool pumps and other appliances before load-shedding starts "to reduce the risk of damage caused when the power comes back on." Switching the geyser off at the DB board before a scheduled outage and back on once the power has settled costs you nothing.
Tripping the earth leakage when it rains
A geyser that only trips in wet weather is almost always telling you that water is getting somewhere electrical. There are two usual routes:
- Through the roof. A slipped tile, a perished flashing or a blocked valley can drip onto the geyser, its isolator switch or the element cover. Water in any of those creates a path to earth, and the earth leakage trips.
- From the geyser itself. A weeping element gasket puts water directly behind the cover plate, next to the thermostat and the wiring. In dry weather the drip may evaporate before it causes trouble, then on a cold, damp day it doesn't.
If your trips line up with Cape winter rain, look at the ceiling around the geyser for stains, and check the drip tray for water when it hasn't been raining. Don't keep resetting the earth leakage until the cause is found: that trip is the device doing exactly what it should.
Never bypass the earth leakage
Moving the geyser to a circuit without earth leakage protection, or disconnecting the earth, gets rid of the trip by removing the protection. The fault is still there, and the next thing to find it may be someone touching a tap. SANS 10142-1 requires the geyser circuit to be on earth leakage of 30 mA or less for exactly this reason.
What you can safely check, and what you can't
Safe for anyone: the breaker and earth leakage on the DB board, the isolator switch, any timer or smart controller, whether the overflow pipe outside is dripping or running hot, whether the ceiling under the geyser is damp, and whether every hot tap is affected or just one.
Leave to a professional: anything behind the element cover plate, including pressing the reset button, testing the element or thermostat, and replacing either. Kwikot states that element replacement "must be done by plumber or electrician," and its thermostat procedures are for "a qualified plumber or installer." Faults in the wiring, the isolator or the DB board are an electrician's job. Under the Electrical Installation Regulations, only a registered person may issue an electrical certificate of compliance, and when a geyser is replaced, the IOPSA/PIRB compliance tables require an electrical CoC for its connection.
When a plumber repairs or replaces a thermostat or element, the same compliance tables require a plumbing certificate of compliance and a written notice of any non-compliance they find on the installation. Ask for both.
Repair or replace?
A failed element or thermostat is a repair, not a new geyser. Both are standard parts. Kwikot recommends replacing them together, because a thermostat stuck closed "leaves the element running continuously", and a new element behind an old thermostat "often means doing the job twice." One visit for both usually works out cheaper than two call-outs.
The answer changes if the tank itself is failing. Rusty water from the hot taps, water coming through the casing or from the bottom of the geyser, or a geyser that is both leaking and tripping are signs the tank is near the end of its life. At that point a new element only buys time. Our guide to what a leaking geyser's leak location tells you covers how to read those signs, and if it has already let go, here is what to do in the first ten minutes.
We test and replace elements and thermostats on site, service geysers, and replace geysers to SANS 10254 when that is the honest answer. Our geyser repair page covers what we handle, and how we quote is set out upfront.
The Durbanville factor
Two local conditions make element and thermostat faults more likely here.
The first is water. Many homes around Durbanville, Vierlanden, D'Urbanvale and the smallholdings toward Philadelphia use borehole or well-point water, and hard water is what bakes scale onto an element. If that's your supply, why your borehole is ruining your geyser explains the problem and the fixes, and the element will thank you for it.
The second is weather. Cape Town gets its rain in winter, and that is when a tired roof or a weeping element gasket shows up as an earth leakage trip. If yours only trips in wet weather, start with the roof above the geyser.
Whatever the symptom, keep the thermostat at 60°C. Running it hotter scales the element faster and wastes heat, and running it lower carries a Legionella risk. Our winter geyser bill guide explains why 60 is the right number. We cover Durbanville, Sonstraal Heights, Kenridge, Eversdal, Vierlanden, Pinehurst, D'Urbanvale, Kraaifontein, Brackenfell and Bellville.
Geyser not heating and tripping FAQs
Why is my geyser not heating up?
Check the geyser's breaker on the DB board, the isolator switch near the geyser and any timer or smart controller first. If all of those are on and the water stays cold, the fault is almost always the element or the thermostat. A burnt-out element stops heating without tripping anything. A failed thermostat stops sending power to the element, and the thermostat's safety cut-out can also trip after overheating or a power surge.
Why does my geyser keep tripping the earth leakage?
The element is insulated from the water around it. When its sheath cracks, current reaches the water and the tank and the earth leakage trips, and Kwikot lists this as a sign of a failed element. Water in the element compartment or the isolator, from a weeping gasket or a roof leak, does the same. Geyser circuits must be on earth leakage that trips at 30 mA or less, so a small leak is enough.
How do I know if my geyser element or thermostat is faulty?
Kwikot's test, done by a qualified plumber with a tester at the element terminals: power at the terminals and cold water means the element has failed; no power at the terminals and cold water means the thermostat has failed. Earth leakage tripping points to the element or to damp wiring, and scalding water points to a thermostat stuck on.
Can I reset my geyser thermostat myself?
We'd advise against it. The reset button sits behind the cover plate next to live terminals, and Kwikot specifies a qualified plumber or installer. The button also only trips for a reason: water above 104°C, a surge over 20 amps, a poor connection or an oversized element. Resetting it without finding the cause usually means it trips again.
How long should a geyser take to heat up?
Heating a full 150 litre tank from about 15°C to 60°C takes roughly 7.9 kWh. On the standard 3 kW element that is about two and a half hours, and on a 4 kW element about two hours, a little longer once heat loss is included. If it has had power for well over three hours and the water is still cold, something is wrong.
Should the element and thermostat be replaced together?
Usually, yes. A thermostat stuck closed leaves the element running non-stop, and Kwikot notes that fitting a new element behind an old thermostat often means doing the job twice. Doing both in one visit costs less than two call-outs.
Written by the team at The Durbanville Plumbers, local plumbers serving Durbanville, Sonstraal Heights, Kenridge, Eversdal, Vierlanden, Pinehurst, D'Urbanvale, Kraaifontein, Brackenfell and Bellville. Heating times and resistance values in this guide are worked from the element rating and are approximate. Treat this as general information, not a substitute for an on-site inspection, and never work on a geyser with the power on.